Strange noise when working in DMR...

Anything specifically related to the DM-1801 version of the firmware
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R9OBQ
Posts: 6
Joined: Thu Apr 02, 2020 12:31 pm

Strange noise when working in DMR...

Post by R9OBQ » Fri May 22, 2020 1:52 pm

Hello again.
The first thing I want to say is that Open DM1801 is the best thing that ever happened to Baofeng DM1801. Convenient management, fast operation, very necessary functions.

But unfortunately, when using it, I encountered a problem: a small and interfering noise. I tried to reproduce this noise and record a video on YouTube. There is no noise when you switch on the transmission, but if you make any sound into the DM 1801 microphone, you will hear noise in the receiver of another radio station. The noise is also heard on other radio stations. Is this a common dm1801 problem? Or was I personally unlucky with this particular radio station?

youtu.be/bPvGeMQ5CwI


PS: just in case, I apologize, English is not my native language...

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kd2lh
Posts: 287
Joined: Mon Dec 02, 2019 2:44 pm

Re: Strange noise when working in DMR...

Post by kd2lh » Sat May 23, 2020 4:43 pm

A couple of possibilities. First, it could be how the vocoder handles the noise. This is not like FM if you're on DMR. A chip is analyzing the sounds it hears and doing compression based on voice elements like silibance.

You might also be hearing the feedback of one to the other as it continues to encode for the first silibance it heard, then picked up from the speaker of the other radio.

Does it perform properly when speaking over DMR?

Marc

R9OBQ
Posts: 6
Joined: Thu Apr 02, 2020 12:31 pm

Re: Strange noise when working in DMR...

Post by R9OBQ » Sun May 24, 2020 5:17 am

The problem is that when turned on, there is no noise in silence. But if I make any sound (for example, the click of a finger), then a decent noise will start. This noise doesn't stop if I'm talking. This noise is more like the noise of a motorway. My correspondents complain about this noise. There is no such noise in FM mode. If I install the original software, the noise is also present, but less pronounced. The effect is very similar to automatic gain control: with a quiet signal, the gain increases, but with a strong signal, it does not go back.

VK3KYY
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Re: Strange noise when working in DMR...

Post by VK3KYY » Sun May 24, 2020 10:02 pm

R9OBQ wrote:
Sun May 24, 2020 5:17 am
If I install the original software, the noise is also present, but less pronounced.
You radio has an electronics hardware fault, probably in the DRM audio path.

Try to get a refund and buy another radio

R9OBQ
Posts: 6
Joined: Thu Apr 02, 2020 12:31 pm

Re: Strange noise when working in DMR...

Post by R9OBQ » Mon May 25, 2020 3:51 am

VK3KYY wrote:
Sun May 24, 2020 10:02 pm
You radio has an electronics hardware fault, probably in the DRM audio path.
Try to get a refund and buy another radio
Unfortunately, it has been more than a month since the purchase, I will not be able to return it. Is there an electrical (or block) circuit on the dm1801 (or gd77) ? I'll try to fix the problem myself...

VK3KYY
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Location: Melbourne, Australia
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Re: Strange noise when working in DMR...

Post by VK3KYY » Mon May 25, 2020 6:17 am

R9OBQ wrote:
Mon May 25, 2020 3:51 am
VK3KYY wrote:
Sun May 24, 2020 10:02 pm
You radio has an electronics hardware fault, probably in the DRM audio path.
Try to get a refund and buy another radio
Unfortunately, it has been more than a month since the purchase, I will not be able to return it. Is there an electrical (or block) circuit on the dm1801 (or gd77) ? I'll try to fix the problem myself...
Try contacting Radioddity, they are often will replace faulty radios

Its strange the problem is only audible on DMR. The mic connection to the DMR chip is via a small switch chip which has 6 pins and could be labelled as U12 on some revisions of the PCB. The switch chip connects the audio to pin 5 of the HR-C6000 DMR DSP chip via a capacitor

However the problem may not be the audio connection from the mic, it may be noise on the 3.3V rail, as this could cause noise to the ADC in the C6000

R9OBQ
Posts: 6
Joined: Thu Apr 02, 2020 12:31 pm

Re: Strange noise when working in DMR...

Post by R9OBQ » Mon May 25, 2020 7:31 am

VK3KYY wrote:
Mon May 25, 2020 6:17 am
Try contacting Radioddity, they are often will replace faulty radios
I didn't buy from an official seller...
VK3KYY wrote:
Mon May 25, 2020 6:17 am
Its strange the problem is only audible on DMR. The mic connection to the DMR chip is via a small switch chip which has 6 pins and could be labelled as U12 on some revisions of the PCB. The switch chip connects the audio to pin 5 of the HR-C6000 DMR DSP chip via a capacitor

However the problem may not be the audio connection from the mic, it may be noise on the 3.3V rail, as this could cause noise to the ADC in the C6000
Thank you for the hint.

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